Introns are the parts of a gene sequence that are not expressed in the protein. In the August 30 issue of Nature Communications, a team led by DOE JGI’s Eukaryote Program head Dan Rokhsar and Uffe Hellsten describe a potential mechanism by which introns have been added to a genome sequence since what they refer to as “the original genomic invasion of introns” millions of years ago. Unlike other previously described mechanisms by which introns have been inserted into a gene sequence, they said, this method does so precisely and without disrupting the surrounding coding sequence.
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The genome of Strongylocentrotus purpuratus was among the sequences compared for this study
(Image by Minette Layne/Wikimedia Commons.)
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“This experiment recapitulates in vivo the birth of an intron that arose in the ancestral jawed vertebrate lineage nearly half-a-billion years ago,” wrote first author Hellsten and his colleagues in the paper. They noted that early eukaryotic genomes had more introns than modern-day eukaryotic genomes. However, they said, the genome of the water flea Daphnia pulex, that the DOE JGI published earlier this year in Science, contained examples of recently-inserted introns.
To understand how a potential intron might be introduced impacting the surrounding coding sequence, the researchers compared a portion of DNA sequence across several genomes – many sequenced by the DOE JGI − including human, platypus, frog, zebrafish, fugu, stickleback, sea urchin and sea anemone.
Hellsten and his colleagues added that the mechanism they described did not match the process by which introns they’d mentioned had been inserted into the Daphnia genome. “This suggests,” they wrote, “that other intron-creation mechanisms besides the one shown here are also active.”